1. Field of the Invention
The present invention relates to a method of crushing silicon blocks, such as blocks of scrap silicon, without contamination of the silicon. More particularly, the present invention relates to a method of crushing, without contamination, blocks of scrap silicon to a size suitable for refining the scrap silicon.
2. Background Art
Recycling of scraps of silicon (scrap silicon) produced during fabrication of semiconductor silicon has been desired. However, for such recycling, impurities, such as dopants, contained in scrap silicon must be removed so as to increase the purity of the silicon. A vacuum refining technique may be employed for increasing the purity of scrap silicon. In this technique, blocks of scrap silicon must be crushed to a smaller size suitable for refining. This is because blocks of scrap silicon come in various shapes and sizes which are difficult to handle. Therefore, blocks of scrap silicon must be crushed to have generally the same size.
Since silicon blocks are very hard, conventionally, silicon blocks are crushed by use of a so-called jaw crusher, which is an ore crusher. At the time of crushing with a jaw crusher, a metal surface of a structural member of the crusher comes into contact with a silicon block, and a metal component from the metal surface adheres to the crushed silicon block. Such adhesion or mixing of metal impurities caused by frictional engagement between the silicon blocks and the structural member cannot be avoided so long as the conventional technique is employed, in which a hard silicon block is crushed through application of a large mechanical force sufficient to crush the block. In the conventional technique, pieces of silicon obtained by crushing of silicon blocks are treated with acid so as to resolve and remove metal impurities adhering to the silicon pieces. However, such metal impurities cannot be completely removed. Accordingly, in order to obtain silicon of high purity, in addition to a vacuum refining process for removing dopants from scrap silicon, another refining process must be performed in order to remove metal impurities adhering to or mixed with pieces of silicon. Therefore, recycling of scrap silicon has been very expensive.